BeforeTheMesh — Programming, Graphics, Geometry for CAE

Step 2

Creating the Rendering Window

A minimal, clean example how to create a rendering window using the platform layer of btm‑framework.

Introduction

Every visualization or mesh‑processing tool begins with a simple requirement: a stable rendering window. Before we can draw meshes, curvature fields, or refinement diagnostics, we need a platform layer that:

creates a native window
initializes an OpenGL context
manages input and events
provides a predictable render loop

In btm‑framework, this responsibility belongs to the platform module, which wraps the OS‑specific details behind a clean C++ interface. This tutorial demonstrates the minimal setup required to create a rendering window using that module.

This tutorial focuses on clarity and minimalism. Later tutorials will show how this window integrates with the framework’s renderer, event system, and visualization utilities.

The Role of the Platform Layer in btm‑framework

The platform layer is the lowest level of the framework. It provides:

Window creation
OpenGL context management
Input handling (keyboard, mouse, window events)
Timing utilities (frame time, delta time)

Higher‑level modules (rendering, mesh visualization, UI overlays) depend on this layer, but the platform module itself remains lightweight and self‑contained.

Minimal Project Structure

For this tutorial, we will create a simple window that iniitializes the platform layer and enters a render loop. The project structure is minimal, consisting of just a single source file:

external/btm-framework/examples/min_rendering_window/main.cpp

This is enough to build a standalone executable that uses the platform layer of btm‑framework.

We will not be using any of the higher‑level rendering or mesh processing modules in this tutorial — just the platform layer to create a window and paint it with a simple background color.

Creating the Window

Below is a minimal example showing how to:

initialize the platform layer
create a window
enter the render loop
clean up on exit

main.cpp

#include "application.h"
#include "glew.h"
#include "timer.h"
#include "window.h"
// this allows us to call functions from the btm‑framework without prefixing
// them with the namespace
using namespace btm;
// This function can be used to render the current state of the simulation
// For example, you could clear the screen, draw objects, etc.
void render() {
    // For demonstration, we'll just clear the screen with a solid color
    // we start the rendering by calling begin_render(), which sets up the
    // OpenGL context for drawing
    begin_render();
    // Set the clear color to black and clear the color and depth buffers
    glClearColor(0.2f, 0.4f, 0.6f, 1.f);
    // clear screen and depth buffer
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    // we finish the rendering by calling end_render(), which swaps the buffers
    // to display the rendered frame and performs any necessary cleanup after
    // rendering
    end_render();
}
// Windows application entry point
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE, LPTSTR, int nCmdShow) {
    // the application instance
    // we are creating a global instance of our application class, which will be
    // used throughout the program this is a GL application, 
    // and we will use it to manage our OpenGL resources and state
    application the_app;
    // initialize the framework
    init_framework();
    // the application instance
    // we are creating a global instance of our application class, which will be
    // used throughout the program this is a GL application, 
    // and we will use it to manage our OpenGL resources and state
    FrameWindow *pFrame = create_main_window(false, 800, 600, "Simple Rendering Window");
    // run the application main loop
    // start the timer before we enter the main loop
    start_timer();
    // call once to initialize elapsed time
    get_elapsed_time();
    // Main message loop
    // pollEvents() is a function that processes Windows messages (like keyboard
    // and mouse input, window events, etc.) and returns true as long as the
    // application should continue running
    while (pollEvents()) {
        // Idle time → render a frame
        // calculate elapsed time since last frame
        float fElapsed = (float)get_elapsed_time();
        // render the scene using the application instance's render method
        render();
        // frame counting mechanism
        {
            static int m_nFrames = 0; // frame Counter
            static float tot = 0;     // time couner
            tot += fElapsed;          // increment counter
            m_nFrames++;
            if (tot >= 1.f) // one second reached
            {
                char txt[200];
                sprintf_s(txt, "Simple Rendering Window, fps:%d", m_nFrames);
                HWND hWnd = pFrame->hWnd;
                // update the window title with the current frames per second
                // (FPS) count SetWindowText is a Windows API function that sets
                // the text of a window's title bar
                SetWindowText(hWnd, txt);
                tot = 0; // reset counters
                m_nFrames = 0;
            }
        }
    }
    // clean up application-specific resources
    the_app.terminate();
    // stop the timer
    stop_timer();

    return 0;
}

The Render Loop

The render loop is the heartbeat of any graphics application. In btm‑framework, it typically:

clears the framebuffer
updates input state
renders the scene
swaps buffers

Keeping this loop minimal is intentional — later tutorials will extend it with:

mesh loading
curvature visualization
debug overlays
GPU‑based refinement diagnostics

What You Should See

When you run the executable, you should see:

a 800×600 window
a blueish background
smooth resizing
a stable framerate

This confirms that the platform layer is working correctly and that the OpenGL context is active.

Next Steps

With the rendering window in place, we can now move to the next tutorial, Step 3: Vectors, Points and Spaces, where we will introduce the fundamental mathematical constructs that underpin all graphics and simulation work: vectors, points, and coordinate spaces.